The present invention relates to fluoride toothpastes using kaolin as the abrasive ingredient. Kaolin is known to be a desirable abrasive for toothpastes because it is inexpensive and because it does clean and polish effectively.
U.S. Pat. No. 4,122,163 discloses a fluoride toothpaste using calcined kaolin as the abrasive. The kaolin used is said to be predominently of the gamma alumina or mullite form. As kaolin is calcined, it undergoes a fairly sharp endothermic reaction at about 520.degree. C., where the kaolin converts to the gamma alumina crystal form. As heating continues, the kaolin undergoes an exothermic reaction at from about 975.degree. to about 990.degree. C. where the crystal form changes from the gamma alumina form to the mullite form.
While the gamma alumina/mullite kaolin employed by Muhler is of a very high degree of purity, having a whiteness index of not more than 10 and a brightness of at least about 93.0, I have found that this kaolin still exerts a detrimental affect on fluoride availability as the toothpaste ages..sup.1 This is surprising because of the high degree of purity of the kaolin. One would expect an adverse impact on fluoride availability due to impurities in the kaolin. However the Muhler patent does not explain why fluoride availability decreases fairly dramatically with aging when the gamma alumina/mullite kaolin is used. FNT .sup.1 Fluoride availability refers to the availability of soluble fluoride ion in the toothpaste composition. To the extent that the fluoride reacts or complexes with other ingredients in the toothpaste, it becomes effectively unavailable for the purpose for which it is intended, i.e., to be taken up by the enamel of the teeth.
While other prior art patents have suggested the use of kaolin as an abrasive in fluoride toothpastes, no such fluoride toothpastes have ever been commercialized, to the best of my knowledge. Prior artisans have heretofore failed to realize the criticality of the combination of factors which I have found necessary in order to make a suitable fluoride toothpaste utilizing a kaolin abrasive.